This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Cyclin dependent kinases (Cdk) are critical regulators of the cell cycle and are upregulated in many cancers. Cks is a Cdk subunit that is known to bind phosphate. We are exploring Cks as a substrate targeting subunit that brings Cdk to substrates already primed by phosphorylation. The specific goal of these crystallographic studies is to solve the structure of Cks bound to phosphopeptides to understand the molecular basis for substrate specificity.